Alternating current switch



Nov. 23, 1954 c. F. SHUNEMANN ALTERNTING CURRENT SWITCH 2 Sheets-Sheet lFiled March 4, 1952 /lll @an H f f77-1E Nov. 23, 1954 c. F. SHUNEMANN2,695,385 ALTERNATING CURRENT SWITCHr l Filed March 4, 1952 2Sheets-snaai 2 az/ alzuzzezzzazzzz b al-5 HZHE United States Patent OALTERNATING CURRENT SWITCH Carl F. Shunemann, Cleveland, Ohio, assignorto Thompson Products, Inc.; Cleveland, Ohio, a corporation of OhioApplication March 4, 1952,- Serial'No-.274,805

14 Claims. (Cl. 333-7) This invention relates to an alternating currentswitch and more particularly .to a switch arranged for connectingtransmission lines or the like without impedance mismatch and withoutintroduction of standing waveson the lines.

lt is an object of this invention to provide an alternat- L,

ing current switch which is simply and-economically con.- structed,which is reliable in operation even at high speeds and which has asubstantially constant characteristic impedance over a range offrequencies so as not to produce an impedance irregularity andassociated ineiicient power transmission.

According to this invention, a switch is provided which is reliable inoperation at high speeds and which, in operative position, forms eithera high-pass or a low-pass filter section. As will appear, such filtersections may have a substantially constant characteristic impedance overa wide range of frequencies and may connect transmission lines, or otherelectrical devices, without an impedance irregularity and the associatedstanding waves and ineicient power transfer.

In one embodiment of this invention, a spring-carried contact issupported within a housing and is r*arranged to be actuated intoengagement with a first conductor insulated from the housing. A secondconductor is connected to the spring-carried contact and the rst andsecond conductors are arranged for connection to terminals oftransmission lines or the like while the housing forms a conductor forconnecting other terminals of the transmission lines. The firstconductor, together with the spring-carried contact structure form alirst inductance and the second conductor is so connected to the contactstructure as to form a second inductance in series with andsubstantially equal to the rst inductance. Support structure for thecontact means is arranged to provide a capacitance from a pointintermediate the first and second inductances to the housing. It will beapparent that this arrangement thereby provides a substantiallysymmetrical low-pass T filter section. As will appear, such a ltersection may have a substantially constant characteristic impedance overa wide range of operating frequencies. It will also be apparent that thespring-carried contact arrangement will be reliable in operation and maybe operated at comparatively high speeds.

lf desired, a plurality of the spring-carried contact arrangements maybe provided for selectively connecting one transmission line to aplurality of lines or to provide a switch for connecting a balanced twoor three-wire transmission line to one or more balanced transmissionlines. It will also be apparent that the above-described arrangement isparticularly adapted for connecting coaxial transmission lines since thehousing forms a conductor and may, if desired, be enclosed so as toeffectively eliminate external radiation.

ln another embodiment of this invention, a conductor is supported withinahousing and is arranged to be actuated into a position closely adjacenta second conductor so as to define therewitha capacitor. Means connectedto the first conductor are arranged in relation to a third conductor todefine therewith a capacitor substantially identical to theabove-mentioned capacitor, and a support structure for the movable rstconductor is arranged to form an inductance from the housing to a pointintermediate the two capacitors so that a substantially symmetricalhigh-pass T filter section is provided. Such a filter section may have asubstantially constant characteristic impedance over a wide range offre- 2,695,385 Patented Nov. 23, 1954 quencies so astoelici'e'ntly'trahsfer power. "It will be apparent that the movable firstconductor, which doesnot make direct contact with the second conductor,Ymay be efficiently and reliably operated at high speeds. 1t will also beapparent that, as with the first embodiment described, sucha'switch"`is'particularly adapted for connectionof coaxiallines and maybe readily duplicated for selective connection' of a plurality of linesor for Switching balanced two or threecouductor lines.

'F his invention contemplates other objects, features and" advantages*which willv become more fully apparent from the following'detailedvdescription taken in conjunction with the accompanying drawings whichillustrate preferred embodiments and in which: i

Figure l is a sectional `view of one form of switch constructedaccording to the principles of this invention; Figure 2 is a sectionalview taken substantially along lines ll-II of Figure l;

Figure 3 is lalsectionalxview taken substantially along lines lll-Ill ofFigure 2; s Figure 4 is a circuit diagram equivalent to a portion of theswitchof-Figure 1;

Figure 5 is a graphical illustration of the relation betweencharacteristic impedance and frequency obtained with'the switch ofFigure 1;

Figure 6 is a graphical illustration of the relation of the voltagestanding wave ratio to frequency obtained with the switch illustrated inFigure l;

Figure 7 is a sectional; view similar to Figure 2, but illustrating amodified switching arrangement;

Figure 8 is asectional `view taken substantially along lines VIII-VIIIof Figure 7;

Figure 9 is a circuit diagram of a portion of the switch of Figures 7and 8 Figure 10 is a graph illustrating the relation betweencharacteristic impedance and frequency obtained with the switch ofFigures 7 and 8; and

Figure 1l is a graph illustrating the relation between voltage standingwave ratio and frequency obtained with the switch modification ofFigures 7 and 8.

A switch assembly constructed according to this invention is generallydesignated by reference numeral 20 in Figure l and includes a pair ofsub-assemblies 21 and 22 each of which is herein arranged to alternatelyconnect one coaxial line to one of two other coaxial transmission lines.This switch is particularly designed as a lobing or sensing switch forcoaxial lines, but it will be understood that the principles of thisinvention may readily apply to many other types of switches.

The switch sub-assemblies 21 and 22 include housings 24 and 25,respectively, the housing 24 herein having a recessed face 26 receivingone face of the housing 25 with a gasket 27 disposed therebetween. Thehousings 24 and 25 may be secured together by any suitable means. Aclging cover 28 is secured to the left face of the housing For actuatingthe switch sub-assemblies 21 and 22, a rotatable shaft 29 is centrallydisposed within the housings 24 and 25 and is arranged to be rotated bymeans of a motor generally designated by reference numeral 29 andAsecured to the right face of the housing 24 by bolts 30. A drive plate31 is secured to a reduced diameter right end portion 32 of the shaft 29by a pin 33 and is connected to the motor 29 by a coupling assemblygenerally designated by reference numeral 34. The drive plate 31 isrotatably supported within an opening in the right-hand face of thehousing 24 through a bearing assembly 36 while a reduced diameter leftend portion 37 of the shaft is rotatably supported within a recess 38 inthe cover plate 28 by a bearing assembly 39.

The housing 24 of the switch sub-assembly 21 herein has peripheralopenings 40, 41 and 42 receiving coaxial linee connectors 43, 44 and 45,respectively. As illustrated, the opening 40 and the connector 43 andthe opening 42 and the connector 45 have mating internal and externalthreads and nuts 46 and washers 47 may be screwed on the connectors totightly secure the same to the housing 24. An alternative connection isillusto the housing 24. The connectors 43, 44 and 45 are Y 3 adapted forconnection to the outside conductors of coaxial liues. For connection tothe inner conductors of coaxial lines, conductors 50, 51 and 52 aresupported by dielectric spacers 53, 54 and 55, respectively, within theconnectors 43, 44 and 45, respectively.

By this invention, means are provided for alternately connecting theconductor 51 to the conductors 50 and 52. -For this purpose, a pair ofarms 57 and 58 are pivotally supported on posts 59 and 60, respectively,within the housing 24. Generally U-shaped resilient spring members 61and 62 are secured to the ends of the arms 57 and 58, respectively, andcarry contacts 63 and 64, respectively, arranged to conductively engageenlarged end portions 65 and 66 of the conductors 50 and 52. The arms 57and 58 are urged toward each other and toward the shaft 29 by a tensioncoil spring 67 secured therebetween. To alternately engage the contacts63 and 64 with the conductor end portions 65 and 66, an eccentric cam 68of a dielectric material is secured to the motor-driven shaft 29,rotation of the shaft serving to alternately cam the arms 57 and 58 intooperative position.l The eccentric 68 is herein disposed in a reduceddiameter recess in the shaft 29 and is held in position by a bowedretaining ring 69 and is held against rotation by a pin 70. i

As shown in Figure 3, plugs 71 and 72 of a suitable dielectric materialare disposed in recesses of the housing 24 and are internally threadedto receive externally threaded end portions of the posts 59 and 60. Thethreaded end portions of the posts 59 and 60, together with the facingsurfaces of the housing and the dielectrics 71 and 72 form a capacitancebetween the binding posts and the housing.

The`binding posts`59 and 60 are connected together and to the conductor,51 by means of a bar 74 disposed between the posts and the lug 75having a bifurcated end portion receiving a central portion of the bar74, the lug being secured to or integral with the conductor 51.

According to this invention, the conductor 51, the lug 75 and the bar 74together define an inductance preferably equal to the inductance definedby each of the arms 57 and 5S and the associated spring 61 or 62 andconductor 50 or 52. For this purpose, the bar 74 is looped intermediatethe lug 75 and the posts 59 and 60 as indicated byreference numerals 77and 7 8, Figure 3, which provides a longer path for current fiow andthereby additional inductance. The conductor 51 may be formedrinto ahelix as indicated by the reference numeral 79 to provide a greaterinductance between the terminal point of the conductor 51 and thebinding post 66. Either the looped portions 77 and 78 or the helixportion 79-may be sufiicient to balance the inductances from the bindingposts 59 and 60 to the end terminals of the conductors 50 and 52,respectively, or they may be utilized in combination as illustrated. Itwill also be apparent that an inductance from the end terminal portionof the conductor 51 to the binding posts 59 and 60 might be provided inother ways obvious to those skilled in the art.

An approximate equivalent circuit of the switch thus far described, ineither operative position, is illustrated in Figure 4 wherein referencenumeral 80 designates an inductance equivalent to the inductance betweenthe terminal end portion of the conductor 51 and the binding post 59 or60, reference numeral 81 designates an inductance equivalent to theinductance between the binding post 59 or 60 and the terminal end of theassociated conductor 50 or 52and reference numeral 82 designates acapacitance equivalent to the capacitance between the threaded endportions of the binding posts 59 and 60 and the housing 24. In practice,this is a good approximation to the actual circuit of the switch sincethe inductances 80 and 81 and the capacitance 82 may be suflicientlygreat with respect to any stray inductances or capacitances for thestray inductances and capacitances to have a negligible value in respectthereto.

It will accordingly be apparent that the switch subassembly 21 thus fardescribed, in either operative position, is effectively a substantiallysymmetrical low-pass T lter section. Figure is a graphical illustrationof the characteristic impedance Zo vs. frequency for such a low-passfilter section. It will be noted that the characteristic impedance Zn issubstantially constant and equal to \/L/ C up to an intermediatefrequency fi after which it gradually increases and approaches zero atthe cut-off frequency fc of the filter. In the formula Zo=\/'L/C, L isthe total series inductance and C is the shunt capacitance.

Figure 6 is a plot of the voltage standing wave ratio VSWR vs. frequencyfor such a filter. Voltage standing wave ratio is conventionally used asa measure of performance of switches and other electrical devices. itwill be noted that the VSWR for such a filter is substantially unity upto the intermediate frequency fi and then gradually increasesapproaching infinity at the cutoff frequency fc. It has been determinedmathematically and confirmed by experiment that the cut-off frequency fcfor such a filter is equal to It will now be apparent that the switchmay have a substantially constant characteristic impedance and a voltagestanding wave ratio substantially equal to unity over a wide range offrequencies by making the cut-ofi frequency fc several times the maximumoperating frequency of the switch. It is, of course, necessary that thecharacteristic impedance Zu be equal to the characteristic impedance ofthe lines connected to the switch to prevent any mis-match andassociated reliections and standing Waves. It may be noted that thegraphs of Figures 5 and 6 are based on the assumption that the switch isterminated in a resistive load equal to the \/L/C.

The two equations Za=\`/L/C and With these equations the switch may bedesigned for optimum performance, keeping in mind that the cut-offfrequency fc should be several times the maximum operating frequency ofthe switch.

The switch sub-assembly 22 may be constructed in a manner substantiallyidentical to the switch-sub-assembly 21, and herein includes a connector8S and an insulated conductor 86 corresponding to the connector 43 andconductor 50 of the sub-assembly 21, a connector 87 and an insulatedconductor 88 corresponding to the connector 45 and conductor 52, arms 89and 9G corresponding to the arms 57 and 58, contacts 91 and 92corresponding to the contacts 63 and 64, posts 93 and 94 correspondingto the posts 59 and 60, an eccentric cam of dielectric material and aconnector and associated conductor (not shown) corresponding to theconnector 44 and conductor 51.

If desired, the two switch sub-assemblies may be used together forswitching of two or three conductor balanced lines. For example, athree-conductor balanced line may be connected to the switch with twoconductors of the line connected to the conductors 52. and 88 and thethird conductor connected to the housing. in such a case, the switch is,in effect, two symmetrical T filter sections in opposed relation to forman H filter section. Other modifications, both in structure and usewill, of course, be apparent to those skilled in the art.

A modified construction is illustrated in Figures 7 and 8. Thisconstruction may be used in an assembly such as illustrated in Figures land 2 in which Figure 7 may be a cross-sectional view corresponding toFigure 2. As shown in Figure 7, this modified switch sub-assembly isgenerally designated by reference numeral 97 and includes a housing 98which may be identical to the housing 24 of the sub-assembly 21, aconnector 99 and a conductor 100 corresponding to ,the connector 43 andconductor 50, a connector 101 and a conductor 102 correspondingv totheyconnector 44 fand.- conductor 51,-

and a connector 103 and conductor 104 corresponding to the connector 45and conductor 52. This modified construction also includes binding posts105 and 106 generally corresponding to the binding posts 59 and 60, arms107 and 108 pivotally mounted on the posts 105 and 106 and a spring 109urging the arms 107 and 108 toward each other and toward a centralmotor-driven shaft 110 corresponding to the shaft 29 of the switchsub-assembly 21. Mounted on the shaft-110 is an eccentric cam member 111of insulating material and held against rotation on the shaft by a pin112. On rotation of the shaft, the eccentric cam 111 alternately movesthe arms 107 and 108 outwardly;

For conduction of alternating current between the arms 107, 108 and theconductors 100, 104, respectively, a pair of plates 114 and 115 areattached to the arms 107 and 108, respectively, and are alternatelymoved into closely spaced relation to plates 116 and 117 on theconductors 100 and 104, respectively. The posts 105 and 106 are operablyconnected to the conductor 102 by means of a connector bar 118 disposedbetween the posts, a plate 119 secured to an intermediate portion of thebar 118.and a plate 120 disposed in closely spaced relation to the plate119 and secured to the conductor 102. The plates 119 and 12.0 deiine acapacitance for conduction of alternating current. This capacitancedefined by plates 119 and 120 is preferably substantially equal to thecapacitance defined by the plates 115 and 117 or the plates 114 vand 116in operative relation, and an inductance is provided from a pointintermediate the capacitances to' the housing. v

Referring to Figure 8, the posts 105 and 106 herein have loopedintermediate portions 121 and 122, respectively, which provide a path ofcurrent flow of increased length and thereby an increased inductance. Asin the case of the irst embodiment described, the posts 105 and 106 havethreaded end portions engaged in internally threaded insulating plugs123 and 124, respectively, which are, in turn, secured in recesses inthe housing 98.

It will be apparent that, from a mechanical standpoint, the constructionfrom Figures 7 and 8 is highly desirable since there is very littlefriction between .the parts in operation and an extremely high speedoperation is possible.

An approximate equivalent circuit of the switch construction of Figures7 and 8 is illustrated in Figure 9 in which capacitance 127 isequivalent to the capacitance provided by plates 119 and 120,capacitance 128 is equivalent to the capacitance defined by the plates114 and 116 or the plates 115 and 117 in operative position, inductance129 is equivalent to Athe inductance defined by the post 105 or the post106, and capacitance 130 is equivalent to the capacitance defined by thethreaded end portions of the post 105 or 106 and the facing surfaces ofthe housing 98, together with the associated dielectric. The circuit ofFigure 9 is a good approximation of the actual circuit defined by theswitch structure of Figure 7 since the capacitances and inductances mayhave values such that stray inductances and capacitances are negligiblein relation thereto.

It will be apparent that the circuit defined by the switch of Figure 7,as illustrated in Figure 9, defines a substantially symmetricalhigh-pass T filter section. Figure is a graphical illustration of thevariation of characteristic impedance of such a lilter section withfrequency. It will be noted that the characteristic impedance Zo issubstantially zero at the cut-off frequency fc and rises with increasingfrequency, being nearly equal to \/L/ C at an intermediate frequency fi,and substantially equal to x/L/ C at frequencies greater than theintermediate frequency fi.

Figure ll is a graphical illustration of the voltage standing wave ratioVSWR plotted against frequency. It will be noted that the voltagestanding wave ratio is substantially infinite at the cut-off frequencyfe and gradually decreases with increasing frequency so that it issubstantially equal to unity at an intermediate frequency f1 and atfrequencies greater than fi. Accordingly, by making the cut-offfrequency fc a fraction of the minimum operating frequency of theswitch, a substantially constant characteristic impedance may beobtained with a voltage standing wave ratio substantially equal to unityover a, wide range of frequencies. g-

6 For design of the switch of Figufes '7 and 8, the following equationsmay be used: f

Z0 lirfc close to fc, M is preferably 0.6, although higher values upl tounity are satisfactory.

T he above equations may be combined to give the lowing equations:

This invention accordingly providesa. switch which may be readilyandecononiically constructed, whichV is reliable in mechanical operationeven at high speeds, and which can be used over a wide range offrequencies without introducing reflections or standing waves andassociated ineicient power transfer.

If desired, the switch of this` invention maybe constructed toapproximate a symmetrical 1r filter section having similarcharacteristiclsto the symmetrical j filter section above described.

Other modifications and Vvariations may, of course, be`

effected without departing from thespirit and scope'of the novelconcepts of the present invention.

I claim as my invention:

l. In an electrical switch for connecting transmission lines or thelike, a housing, at least arpair of conductors insulated from saidhousing each arranged' for connection to one terminal of a line,me'ans'for connecting other terminals of lines to said housing, means insaid housing connecting said conductorsl including switch meansactuatable to transmit alternating current, support' means affixed insaid housing and'connected to said connecting means at an intermediatepoint between said conductors, said connecting means and said conductorsbeing constructed and arranged to provide substantially equal seriesreactances at either side of said intermediate point, and

said support means being constructed and arranged tov series reactancesto thereby provide a substantially symmetrical T iilter section.

2. In an electrical switch for connecting transmission lines or thelike, a housing, at least a pair of conductors insulated from saidhousing each arranged for connection to one terminal of a line, meansfor connecting other terminals of lines to said housing, means in saidhousing connecting said conductors including switch means actuatable totransmit alternating current, said connecting means and said conductorsbeing constructed and arranged to provide series capacitances, andsupport means aixed in said housing and connected to said connectingmeans, said support means being constructed and arranged to provide aparallel inductance cooperating with said series capacitances to definea high-pass filter section pass band thereof.

' 3. In an electrical switch, a housing, at least two conductorsinsulated from said housing, support means aiiixed in said housing,switch means movably supported on said support means and actuatable intoan operative position in alternating current conductive relation withrespect to one of said conductors, means connecting said switch means toanother of said conductors for transmission of alternating currenttherebetween, said switch means together with said one conductor havinga predetermined reactance in said operative position of said switchmeans, said connecting means and said another conductor beingconstructed and arranged to provide a reactance substantially equal tosaid predetermined reactance, and said support means providing areactance of opposite sense with respect to the above-mentionedreactances to thereby provide a substantially symmetrical T filtersection.

4. In an electrical switch, a housing, at least two conductors insulatedfrom said housing, support means affixed in said housing, switch meansmovably supported in said support means and actuatable into an operativeposition in alternating current conductive relation with respect to oneof said conductors, said switch means together with said one conductordefining a first inductance, means connecting said switch means toanother of said conductors for transmission of alternating currenttherebetween and defining therewith an inductance substantially equal tosaid first inductance, and said support means providing a capacitancethereby providing a substantially symmetrical low-pass T filter section.

5. In an electrical switch, a housing, at least two conductors insulatedfrom said housing, support means atiixed in said housing, switch meansmovably supported on said support means and actuatable into an operativeposition in alternating current conductive relation with respect to oneof said conductors, said switch means together with said one conductordefining a first capacitance, means connecting said switch means toanother of said conductors and defining therewith a capacitancesubstantially equal to said first capacitance, and said support meansdefining an inductance thereby providing a substantially symmetricalhigh-pass filter.

6. In an electrical switch, a housing, at least two conductors insulatedfrom said housing, a post affixed in said housing, a switch memberpivotal on said post and actuatable into an operative position inalternating current conductive relation to one of said conductors, andmeans connecting said post to another of said conductors, said switchmember together with said one conductor defining a first reactance, saidconnecting means together with said another conductor defining a secondreactance substantially equal to said first reactance, and said postproviding a reactance of opposite sense with respect to theabove-mentioned reactances to thereby provide a substantiallysymmetrical T filter,

7. ln an electrical switch, a housing, at least two conductors insulatedfrom said housing, a post afiixed in said housing, a switch memberpivotal on said post and actuatable into an operative position inalternating current conductive relation to one of said conductors, andmeans connecting said post to another of said conductors, said switchmember together with said one conductor defining a first inductance,said connecting means together with said another conductor defining asecond inductance substantially equal to said first inductance, and saidpost providing a capacitance to thereby provide a substantiallysymmetrical low-pass filter.

8. In ari electrical switch, a housing, at least two conductorsinsulated from said housing, a post aixed in said housing, a switchmember pivotal on said post and actuatable into an operative position inalternating current conductive relation to one of said conductors, andmeans connecting said post to another of said conductors, said switchmember together with said one conductor defining a first capacitance,said connecting means together with said another conductor defining asecond capacitance substantially equal to said first capacitance, andsaid post providing an inductance to thereby provide a substantiallysymmetrical high-pass filter.

9. In an electrical switch, a housing, at least two insulated conductorsin said housing, a post, means supporting said post in said housing, anarm pivotal on said post, means for actuating said arm between operativeand inoperative positions, said arm having means thereon cooperatingwith one of said conductors to establish alternating current conductiverelation therebetween in said operative position of said arm, meansconnecting said post to the other said conductors for conducting of atleast alternating current, said arm together with said one conductordefining a first reactance, said connecting means together with saidother conductor defining a second reactance substantially equal to saidfirst reactance, and said supporting means and said post defining athird reactance between said housing and a point intermediate said armand said connecting means to thereby provide a substantially symmetricalreactive T filter section.

10. ln an electrical switch, a housing, at least two insulatedconductors in said housing, a post, means supporting said post in saidhousing, an arm pivotal on said post,- means for actuating said armbetween operative and inoperative positions, said arm having meansthereon cooperating with one of said conductors to establish alternatingcurrent conductive relation therebetween in said operative position ofsaid arm, means connecting said post to the other said conductors forconducting of at least alternating current, said arm together with saidone conductor defining a first inductance, said connecting meanstogether with said other conductor defining a second inductancesubstantially equal to said first inductance, and said supporting meansand said post defining a capacitance between said housing and a pointintermediate said arm and said connecting means to thereby provide asubstantially symmetrical low-pass T filter section.

11. In an electrical switch, a housing, at least two insulatedconductors in said housing, a post, means supporting said post in saidhousing, an arm pivotal on said post, means for actuating said armbetween operative and inoperative positions, said arm having meansthereon cooperating with one of said conductors to establish alternatingcurrent conductive relation therebetween in said operative position ofsaid arm, means connecting said post to the other said conductors forconducting of at least alternating current, said arm together with saidone conductor defining a first capacitance, said connecting meanstogether with said other conductor defining a second capacitancesubstantially equal to said first capacitance, and said supporting meansand said post defining an inductance between said housing and a pointintermediate said arm and said connecting means to thereby provide asubstantially symmetrical high-pass T filter section.

12. ln an alternating current electrical switch for connectingtransmission lines or the like and operating over a range offrequencies, a housing, at least two conductors adapted forV connectionto said line and insulated from said housing, support means affixed insaid housing, switch means movably supported on said support means andactuatable into alternating current conductive relation with respect toone of said conductors, and alternating current conductive connectionmeans between said support means and the other of said conductors, saidswitch means together with said one conductor defining a firstinductance, said connection means together with said other conductordefining a second inductance substantially equal to said firstinductance, and said support means defining a capacitance between saidhousing and a point intermediate said inductances substantiallyaccording to the formulas L and C:

i switch means movably supported on said support means and actuatableinto alternating current conductive relation with respect to one of saidconductors and alternating current conductive connection means betweensaid support means and the other of said conductors, said switch meanstogether with said one conductor defining a rst capacitance, saidconnection means together with said other conductor defining a secondcapacitance, and said support means dening an inductan and a thirdcapacitance in series between said housing and a point intermediate saidcapacitances, substantially according to the formulas where L is saidinductance, C1, C2 and C3 are said rst, second and third capacitances,respectively, Zo is the characteristic impedance of said transmissionlines and fc is the frequency less than the minimum operating frequencyof the switch.

14. A switch assembly comprising: a pair of subassemblies each includinga housing; iirst, second and third conductors insulated from saidhousing; said support means in said housing; switch means movable onsaid support means and actuatable alternately into con- 0 Number ductiverelation to said first and second conductorsgrand means connecting saidswitch means to said third conductor; said switch means and each of saidfirst and second conductors in conductive relation together dening a rstreactance; said connecting means and said third conductor defining asecond reactance substantially equal to said first reactance; and saidsupport meansdefining a third reactance between said housing and a pointintermediate said first and second reactances; each sub-assembly ineither aperture position of said switch means thereby defining asubstantially symmetrical reactive T filter section; and said housingsof said pair of sub-assemblies being connected together to connect saidT lter sections in opposed relation thereby to define substantiallysymmetrical reactive H filter-sections.

References Cited in the file Vof this patent UNITED STATES PATENTS NameDate Chaffee Mar. 18, 1941 Patterson Dec. 3, 1946 Creaser June 24, 1952

